Influence of two structural phases of Fe3O4 and [gamma]-Fe2O3 on the properties of polyimide/iron oxide composites

Partially aliphatic polyimide/iron oxide composites based on the poly(amic acid) from 5-(2,5-dioxotetrahydro-3-furyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride and 4,4'-oxydianiline with iron oxide in different weight percentages were obtained. The structural phases of the transition of magnetite to maghemite occurring in these composites, at different temperatures, are discussed. The physical characteristics, including magnetic, thermal, structural and morphological properties, evaluated using X-ray diffraction, scanning electron microscopy and thermal analysis, are influenced by the interplay of the filler content and the structural changes of the composite. The X-ray diffraction patterns of all samples show a cubic structure indexed as magnetite (Fe3O4) or maghemite ([gamma]-Fe2O3). Quantification of these two phases was evidenced by the Rietveld method. The electrical properties analysed under different humidity conditions evidence the potential applicability of these polyimide/iron oxide materials as humidity sensors. © 2015 Society of Chemical Industry